Free bilirubin concentrations and bilirubin-binding affinity in term and preterm infants

doi:10.1016/S0022-3476(80)80860-2

The Journal of Pediatrics

Volume 96, Issue 3, Part 2, March 1980, Pages 521-527

https://doi.org/10.1016/S0022-3476(80)80860-2 Get rights and content

Free bilirubin concentration, bilirubin-binding capacity, and bilirubin-binding affinity were determined hy peroxidase oxidation in 66 newborn infants. Twelve healthy term infants whose unconjugated bilirubin concentration was 15.8±3.7 mg/dl (mean±SD) had a binding capacity of 31.9±3.7 mg/dl (bilirubin: albumin molar ratio=0.89±0.07) and Ka=28±11×10⁷/M. Twelve term infants with clinical complications of asphyxia, acidosis, respiratory distress, or sepsis, and 17 preterm infants with no complications had lower serum albumin concentrations and slightly reduced binding capacity and affinity compared to the healthy term infants. Free bilirubin concentrations were similar in these three groups, averaging 8 to 9 nmol/l in each group. Twenty-five preterm infants with complications had significantly higher free bilirubin (19±11 nmol/l), lower binding capacity, and lower binding affinity than any of the other three groups (P<0.01 for all comparisons) Five of the 25 sick preterm infants had kernicterus at autopsy. These five infants were similar to the other 20 in birth weight, gestational age, serum bilirubin, and serum albumin level, but had significantly higher free bilirubin and significantly lower binding capacity and affinity. The data suggest that serious neonatal, illness is associated with a marked reduction in bilirubin-binding capacity and affinity and an increased risk of kernicterus in preterm infants. The mechanism by which neonatal morbidity decreases bilirubin binding is not known.

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Cited by (42)

Bilirubin-Displacing Effect of Ceftriaxone in Infants With Unconjugated Hyperbilirubinemia Born at Term
2023, Journal of Pediatrics
Citation Excerpt :
These developmental changes in Ka and bilirubin-binding capacity may predispose infants born premature to greater risk for a bilirubin displacing effect and may explain the reported displacing effect with use of ceftriaxone.23 A major strength of the study is the prospective assessment with infants serving as their own controls, thus eliminating sepsis and unknown confounders.23,25,26 Sepsis is known to negatively influence Ka.
To evaluate the effect of intravenous (IV) ceftriaxone on free bilirubin concentrations in infants with unconjugated hyperbilirubinemia born at term.
A prospective study was performed with subjects serving as their own controls. Our inclusion criteria were infants born at term <7 days old with sepsis and receiving IV antibiotics for >3 days and resolving hyperbilirubinemia with total serum bilirubin levels between 6 and12 mg/dL by day 4 of life. Free bilirubin concentrations were measured by the peroxidase method using a UB analyzer and a Zone Fluidics device before (baseline) and 15 minutes after (follow-up) IV ceftriaxone administration on postnatal days 4 to 6. Paired measurements of free bilirubin were analyzed using a Student paired t-test or Wilcoxon signed-rank test.
In total, 27 infants were studied. The mean free bilirubin (μg/dL) at follow-up was not different from that at baseline when measured by the UB analyzer (P = .78). The mean free bilirubin was significantly lower at follow-up compared with baseline when measured by the Zone Fluidics device (P = .02). The ratio of a free bilirubin with and without ceftriaxone, an index of displacing effect, was 1.02 (95% CI 0.89-1.14) using the UB analyzer and 0.58 (95% CI 0.30-0.86) using the Zone Fluidics device.
Ceftriaxone is not associated with a bilirubin-displacing effect in infants with a mild unconjugated hyperbilirubinemia. Home therapy with once-daily intramuscular ceftriaxone may be an alternative option for management of sepsis in asymptomatic infants with a mild unconjugated hyperbilirubinemia born at term.
Bilirubin Albumin Binding and Unbound Unconjugated Hyperbilirubinemia in Premature Infants
2018, Journal of Pediatrics
Citation Excerpt :
However, more importantly, our findings suggest that the peak UB, the primary determinant of neurotoxicity, is associated primarily with a concomitant decrease in binding affinity and that this association is modified by the degree of prematurity and is seen mainly in premature infants ≤30 weeks GA. In premature infants, variability in bilirubin binding affinity has been reported previously using the Sephadex gel filtration method.13 Our study findings also suggest variability in bilirubin binding affinity among premature infants but also improvement in bilirubin binding affinity with increasing GA, indicating a maturational process for binding affinity.
To evaluate the associations between unbound bilirubin (UB) and total serum bilirubin (TSB), bilirubin:albumin molar ratio (BAMR), and bilirubin albumin binding affinity (Ka) as a function of gestational age (GA) in infants born at 24-33 weeks GA.
In a prospective observational study, TSB and UB were measured twice daily at least 8 hours apart during the first postnatal week. Serum albumin was measured to calculate BAMR on each day. The highest UB on each day, corresponding TSB, and serum albumin were used to calculate the Ka on each day.
For the 166 infants studied, peak UB significantly correlated with concomitant Ka (r = −0.44, P = .001) but not with concomitant TSB or BAMR after adjusting for GA. On multiple regression analyses, there was a significant association of concomitant Ka (−0.06, 95% CI −0.08 to −0.04, P = .0001), but not concomitant TSB or BAMR with peak UB after controlling for GA, birth weight, race, and sex. GA group was a significant effect modifier for the association between Ka and peak UB (0.03, 95% CI 0.02-0.04, P < .001). Interaction analyses showed the association between concomitant Ka and peak UB was significant for the 24-30 weeks GA group infants, but not for the 30^1/7-33 weeks GA group infants.
Peak UB was primarily associated with a decrease in binding affinity in infants ≤30 weeks GA. Interventions aimed at improving binding affinity may be important in decreasing the risk of bilirubin-induced neurotoxicity.
Unconjugated free bilirubin in preterm infants
2017, Early Human Development
Citation Excerpt :
UCBfree can translocate across the blood-brain barrier [7,8], where it may induce apoptosis and necrosis in specific brain areas [8,9]. Preterm infants, especially when ill, may have high UCBfree levels, partly attributable to a low bilirubin-albumin binding affinity (Ka) compared to term infants [10,11]. The UCBfree/TSB ratio, which represents the combination of magnitude (represented by TSB) and distribution (represented by UCBfree) of the accumulated bilirubin load, has been proved to correlate better with automated auditory brain stem response than either UCBfree or TSB alone and is suggested to be the best BIND predictor [12].
Hyperbilirubinemia guidelines are based on total serum bilirubin (TSB), in combination with either gestational age (GA) or birth weight (BW), postnatal age and specific risk factors. However, TSB is a poor predictor of bilirubin-induced neurotoxicity (BIND). Free unconjugated bilirubin (UCBfree) and the UCBfree/TSB ratio are more directly related to BIND, but data on their postnatal courses are unknown.
To characterize the postnatal courses of UCBfree and UCBfree/TSB ratio, and assess their relationships with clinical characteristics.
72 preterm infants ≤ 32 weeks GA, admitted to the University Medical Center Groningen, The Netherlands.
During the first postnatal week, bilirubin plasma parameters were analyzed and their relationship with clinical parameters was analyzed. Postnatal changes were analyzed using Generalized Estimating Equations. Data are expressed as medians [ranges].
Less than 10% of the cohort (GA: 29 [26–31] weeks; BW: 1165 [600–1975] g) showed hyperbilirubinemic risk factors. We observed a large variation in UCBfree (27 [1–197] nmol/L), that could partly be explained by postnatal age and gender, but not by other risk factors. Maximal UCBfree levels of 50 [13–197] nmol/L occurred at day 4 and were higher in males. In contrast to TSB, UCBfree/TSB ratios (0.19 [0.01–1.04]) were higher in infants with low GA/BW.
UCBfree levels vary considerably in preterm infants, despite a low incidence of hyperbilirubinemic risk factors and similar TSB-based phototherapy treatment. UCBfree could not be predicted by GA or BW, but UCBfree/TSB ratios are highest in the smallest preterms, while they have the lowest TSB levels.
Bilirubin Binding Capacity in the Preterm Neonate
2016, Clinics in Perinatology
Citation Excerpt :
In a large, prospective study using the modified peroxidase method, Amin and colleagues49 reported that in more mature preterm infants (>30 weeks GA), the binding affinity improves over the first week, whereas in infants less than 30 weeks GA, bilirubin-binding affinity varies within and between infants, but overall, decreases during the first postnatal week. This variability in bilirubin binding affinity in premature infants has been reported previously using the Sephadex method.45 Several exogenous and endogenous factors described elsewhere in this paper may contribute to this variability in bilirubin binding affinity in premature infants.
Biology of Bilirubin Photoisomers
2016, Clinics in Perinatology
The enigma of low bilirubin kernicterus in premature infants: Why does it still occur, and is it preventable?
2014, Seminars in Perinatology
Citation Excerpt :
Limited innate albumin–bilirubin binding and clinical conditions that impair albumin–bilirubin-binding capacity are 2 such factors. The albumin–bilirubin binding constant varies significantly between newborns17,22 and as a function of postnatal age.23,24 Bilirubin-binding capacity is reduced in sick unstable infants25–27 and is adversely affected by the presence of competing compounds23,28–30 including unbound free fatty acids.31,32
Low bilirubin kernicterus in preterm neonates, though rare, remains an unpredictable and refractory form of brain injury. Hypoalbuminemia, co-morbid CNS insult(s), infection, and inflammation are contributing causes that, in many cases, appear to interact in potentiating bilirubin neurotoxicity. Despite compulsive attention to serum bilirubin levels, and clinical and laboratory indices of neurotoxicity risk, low bilirubin kernicterus continues to be seen in contemporary NICUs. While efforts to refine and improve current treatment guidelines are certainly needed, such revision(s) will also have to take into account the risks and benefits of any intervention, including phototherapy.

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^*: Supported in part by a grant from the Charles H. Hood Foundation, Boston, and by Diabetes Research Center Grant HD 11343, National Institute for Child Health and Human Development, National Institute of Health.

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Free bilirubin concentrations and bilirubin-binding affinity in term and preterm infants*

J Pediatr

J Pediatr

J Pediatr

J Pediatr

Clin Chem Acta

J Biol Chem

FEBS Lett

A rapid micromethod for measuring the reserve albumin binding capacity in serum from newborn infants with hyperbilirubinemia

J Lab Clin Med

Sephadex G-25 quantitative estimation of free bilirubin potential in newborn infants' sera: A guide to the prevention of knernicterus

J Lab Clin Med

Clinical evaluation of Sephadex gel filtration in estimation of bilirubin binding in serum in neonatal jaundice

Arch Dis Child

Determination of unbound bilirubin in the serum of newborns

Clin Chem